Yup.  Grit is just small, hard rocks.  Free range chickens in most environments should be able to pick it up off the ground.  Those that are restricted to a coop and smallish run all or most of the time need the extra access.  In any case, grit is inexpensive and making it available doesn't hurt anything.  They'll only peck at it if they want to.
This artificial replacement of natural grit also explains why we have multiple sized grits for chicks vs. adults.  In the outdoors, the birds can peck at whatever sized rock appeals to them.  The chicks would mostly take in smaller particles, while larger birds would take in more pebble-sized bits.